In recent years head-up displays (HUDs) have become an increasingly popular mechanism for displaying information to an operator of a vehicle, such as an aircraft. One of the primary reasons for the increasing demand for HUDs is that the information may be displayed to the operator while the operator looks through his or her windshield. That is, the operator does not need to look away from the windshield in order to view the desired information.
Typical HUD systems often include a display device, such as a cathode ray tube (CRT), an optics array (typically including several lenses), and an image combiner. Established performance expectations for HUDs have evolved based on these CRT systems. Certain more recent HUD systems have begun to include a liquid crystal display (LCD) panel and a backlight as the display device. In an LCD HUD system, light from the backlight passes through the LCD panel to create the desired image, and the optics array focuses the image to a desired apparent viewing distance and displays it on the image combiner, which is typically a transparent screen on which the image is displayed while the operator simultaneously views the outside world therethrough. The image is sometimes referred to as being focused on the combiner even though the apparent focus is design dependent and does not necessarily coincide with the location of the image combiner. Often, the HUD image is adjusted to be substantially collimated, for example with the apparent focus at a distant location. In such implementations, this focused image is incident on and reflected by the combiner.
Due to various imperfections in the design and manufacturing of the components of the HUD systems, the image displayed on the image combiner often exhibits variations in brightness and/or color across the viewable surface area of the image combiner. More particularly, various portions of the light propagating from the image combiner to the user have differing values of radiant properties, such as luminance and frequency. These variations increase the difficulty in optimizing system performance. For example, if particular portions of the image displayed on the image combiner are too bright, the operator may be distracted. However, if portions of the image are too dim, the operator will not be able to see them at all.
Accordingly, it is desirable to provide a system and method for optimizing image uniformity on a head-up display. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.